VF displays are commonly used in emissive instrumentation applications such as in the instrument panel of a motor vehicle. The light emitted by the display is produced by electron bombardment of phosphor materials. A conventional VF display, depicted in FIGS. 1-3, comprises one or more relatively low potential filaments or cathodes, one or more relatively high potential phosphored anodes which define a phosphored graphic pattern, and a relatively high potential grid disposed between the filaments and the phosphored anodes. Electrons boiled off the filaments are attracted by the grid and driven into the phosphored anodes, resulting in emission of light at the phosphor surface.
The color of the light emitted from a VF display is determined by the chemical composition of the phosphor. The most commonly used phosphors emit bluish-green light since such phosphors are long lasting, and emit relatively bright light with low potential (such as 12 VDC) electron bombardment. As a result, it has been difficult to provide multicolor graphic patterns in a VF display without resorting to unproven or exotic phosphor materials and relatively high driving voltages. Attempts at filtering the bluish-green light to other colors such as yellow or red, have not been acceptable due to the reduced intensity of the filtered light. Undesirable parallax effects come into play if bezels or light-piping techniques are used to position graphic patterns in front of the display.